BACKGROUND: The ferlin gene family possesses a rare and identifying featureconsisting of multiple tandem C2 domains and a C-terminal transmembrane domain.Much currently remains unknown about the fundamental function of this genefamily, however, mutations in its two most well-characterised members, dysferlin and otoferlin, have been implicated in human disease. The availability of genome sequences from a wide range of species makes it possible to explore the evolutionof the ferlin family, providing contextual insight into characteristic featuresthat define the ferlin gene family in its present form in humans. RESULTS: Ferlingenes were detected from all species of representative phyla, with two ferlinsubgroups partitioned within the ferlin phylogenetic tree based on the presenceor absence of a DysF domain. Invertebrates generally possessed two ferlin genes(one with DysF and one without), with six ferlin genes in most vertebrates (threeDysF, three non-DysF). Expansion of the ferlin gene family is evident between thedivergence of lamprey (jawless vertebrates) and shark (cartilaginous fish).Common to almost all ferlins is an N-terminal C2-FerI-C2 sandwich, a FerB motif, and two C-terminal C2 domains (C2E and C2F) adjacent to the transmembrane domain.Preservation of these structural elements throughout eukaryotic evolutionsuggests a fundamental role of these motifs for ferlin function. In contrast,DysF, C2DE, and FerA are optional, giving rise to subtle differences in domaintopologies of ferlin genes. Despite conservation of multiple C2 domains in allferlins, the C-terminal C2 domains (C2E and C2F) displayed higher sequenceconservation and greater conservation of putative calcium binding residues acrossparalogs and orthologs. Interestingly, the two most studied non-mammalian ferlins(Fer-1 and Misfire) in model organisms C. elegans and D. melanogaster, present asoutgroups in the phylogenetic analysis, with results suggestingreproduction-related divergence and specialization of species-specific functions within their genus. CONCLUSIONS: Our phylogenetic studies provide evolutionaryinsight into the ferlin gene family. We highlight the existence of ferlin-likeproteins throughout eukaryotic evolution, from unicellular phytoplankton andapicomplexan parasites, through to humans. We characterise the preservation offerlin structural motifs, not only of C2 domains, but also the more poorlycharacterised ferlin-specific motifs representing the DysF, FerA and FerBdomains. Our data suggest an ancient role of ferlin proteins, with lessons fromvertebrate biology and human disease suggesting a role relating to vesicle fusionand plasma membrane specialization.